Work implement of hydraulic excavator and method of manufacturing work implement of hydraulic excavator

ABSTRACT

The number of steps required for a welding operation of a work implement of a hydraulic excavator is reduced while the welding quality is improved. A boom includes a top plate, a left side plate joined to the top plate, and a boom foot bracket. The boom foot bracket includes an extending portion. The extending portion includes a portion that faces a side surface of the top plate.

TECHNICAL FIELD

The present invention relates to a work implement of a hydraulic excavator and a method of manufacturing the work implement of the hydraulic excavator.

BACKGROUND ART

Conventionally, regarding a work implement of a hydraulic excavator, there has been a proposed technique by which welding is performed along a line formed between a dam and the abutting surface of a plate material divided along the border with the dam to thereby form a weld bead along the line (for example, see Japanese Patent Laying-Open No. 2015-151741 (PTD 1)).

CITATION LIST Patent Literature PTL 1: Japanese Patent Laying-Open No. 2015-151741 SUMMARY OF INVENTION Technical Problem

When each of members constituting a work implement of a hydraulic excavator is joined by welding, it is desirable to form a continuous weld line for the purpose of reducing the number of steps required for the welding operation and for improving the welding quality.

An object of the present invention is to provide a work implement of a hydraulic excavator, for which the number of steps required for a welding operation can be reduced and also the welding quality can be improved.

Solution to Problem

A work implement of a hydraulic excavator according to the present invention includes: a first plate material; a second plate material joined to the first plate material; a third plate material joined to the first plate material and facing the second plate material at a distance from the second plate material; and a fourth plate material joined to the second plate material and the third plate material and facing the first plate material at a distance from the first plate material. The first plate material, the second plate material, the third plate material, and the fourth plate material are joined to one another to form a box-shaped structure body. The work implement of the hydraulic excavator further includes a first attachment member joined to each of the first plate material, the second plate material, the third plate material, and the fourth plate material at an end of the box-shaped structure body in a longitudinal direction of the box-shaped structure body. The first attachment member includes an extending portion that extends in the longitudinal direction of the box-shaped structure body. The extending portion includes a portion that faces a side surface of the first plate material.

A manufacturing method according to the present invention is a method of manufacturing a work implement of a hydraulic excavator. The work implement of the hydraulic excavator includes: a first plate material; a second plate material joined to the first plate material; a third plate material joined to the first plate material and facing the second plate material at a distance from the second plate material; and a fourth plate material joined to the second plate material and the third plate material and facing the first plate material at a distance from the first plate material. The first plate material, the second plate material, the third plate material, and the fourth plate material are joined to one another to form a box-shaped structure body. The work implement of the hydraulic excavator further includes a first attachment member joined to each of the first plate material, the second plate material, the third plate material, and the fourth plate material at an end of the box-shaped structure body in a longitudinal direction of the box-shaped structure body. The first attachment member includes an extending portion that extends in the longitudinal direction of the box-shaped structure body. The extending portion includes a portion that faces a side surface of the first plate material. The manufacturing method includes: forming a recess portion as a partial recess in a surface of the first attachment member, the recess portion being located between the extending portion and the side surface of the first plate material that faces the extending portion; and filling up the recess portion by welding.

Advantageous Effects of Invention

According to the present invention, the number of steps required for the welding operation of the work implement of the hydraulic excavator can be reduced while the welding quality can be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating the external appearance of a hydraulic excavator according to an embodiment.

FIG. 2 is a side view showing the schematic configuration of a boom shown in FIG. 1.

FIG. 3 is a cross-sectional view of the boom taken along a line III-III shown in FIG. 2.

FIG. 4 is an enlarged perspective view of a region IV in FIG. 2.

FIG. 5 is an enlarged perspective view showing a part of a top plate.

FIG. 6 is a perspective view showing the configuration of a boom foot bracket.

FIG. 7 is a plan view of region IV in FIG. 2.

FIG. 8 is a side view of region IV in FIG. 2.

FIG. 9 is a perspective view showing the state where the top plate and the boom foot bracket are welded to each other.

FIG. 10 is a perspective view showing the state where the top plate and the boom foot bracket are welded to each other, as seen at a different angle.

FIG. 11 is a side view showing the schematic configuration of an arm shown in FIG. 1.

DESCRIPTION OF EMBODIMENTS

In the following, a work implement of a hydraulic excavator and a method of manufacturing the work implement of the hydraulic excavator according to an embodiment will be described. In the following description, the same components are designated by the same reference characters. Names and functions thereof are also the same. Accordingly, the detailed description thereof will not be repeated.

FIG. 1 is a diagram illustrating the external appearance of a hydraulic excavator 100 according to an embodiment.

Hydraulic excavator 100 mainly includes a traveling unit 1, a revolving unit 3, and a work implement 4. The main body of the hydraulic excavator is formed of traveling unit 1 and revolving unit 3. Traveling unit 1 includes a pair of crawler belts on the right and left sides. Revolving unit 3 is mounted in traveling unit 1 via a revolving mechanism in an upper portion of traveling unit 1. Revolving unit 3 includes an operator's cab 8.

Work implement 4 is pivotally supported on revolving unit 3 so as to be operable in the up-down direction, and configured to perform such work as excavation of soil. Work implement 4 includes a boom 5, an arm 6, and a bucket 7. Boom 5 has a base portion that is coupled to revolving unit 3. Arm 6 is coupled to an end of boom 5. Bucket 7 is coupled to an end of arm 6. Each of boom 5, arm 6 and bucket 7 is driven by a hydraulic cylinder, so that work implement 4 can be driven.

FIG. 2 is a side view showing the schematic configuration of boom 5 shown in FIG. 1. FIG. 3 is a cross-sectional view of boom 5 taken along a line III-III shown in FIG. 2. As shown in FIGS. 2 and 3, boom 5 has a top plate 11, a left side plate 12, a right side plate 13, and a bottom plate 14. As shown in FIG. 3, left side plate 12 and right side plate 13 are joined at their upper ends to top plate 11 by welding and also joined at their lower ends to bottom plate 14 by welding. Right side plate 13 faces left side plate 12 at a distance from left side plate 12. Left side plate 12 and right side plate 13 are disposed approximately in parallel with each other. Bottom plate 14 faces top plate 11 at a distance from top plate 11. Top plate 11 and bottom plate 14 are disposed approximately in parallel with each other.

As shown in FIG. 3, top plate 11, left side plate 12, right side plate 13, and bottom plate 14 are joined to one another to form a box-shaped structure body 19. A weld bead 111 is formed in a portion where top plate 11 and left side plate 12 are joined to each other. A weld bead 112 is formed in a portion where top plate 11 and right side plate 13 are joined to each other. A weld bead 113 is formed in a portion where left side plate 12 and bottom plate 14 are joined to each other. A weld bead 114 is formed in a portion where right side plate 13 and bottom plate 14 are joined to each other.

Collectively referring to FIG. 2, top plate 11, left side plate 12, right side plate 13, and bottom plate 14 each have an elongated plate shape. Box-shaped structure body 19 is formed as an elongated structure body extending in the longitudinal direction of boom 5. The longitudinal direction of box-shaped structure body 19 corresponds to the direction perpendicular to the surface of the sheet of paper showing FIG. 3

As shown in FIG. 2, a boom foot bracket 15 is joined to one end of box-shaped structure body 19 in its longitudinal direction. Also, an arm attachment bracket 16 is joined to the other end of box-shaped structure body 19 in its longitudinal direction. Boom foot bracket 15 and arm attachment bracket 16 are joined to one end and the other end, respectively, of box-shaped structure body 19 in its longitudinal direction so as to be connected to each of top plate 11, left side plate 12, right side plate 13 and bottom plate 14. Boom foot bracket 15 forms the rear end portion of boom 5 while arm attachment bracket 16 forms the front end portion of boom 5. Boom foot bracket 15 is coupled to revolving unit 3 via a pin. Arm 6 is coupled to arm attachment bracket 16 via a pin.

In the embodiment, the direction in which top plate 11 and bottom plate 14 are aligned (the up-down direction in FIG. 3) is referred to as an up-down direction. The direction in which left side plate 12 and right side plate 13 are aligned (the right-left direction in FIG. 3) is referred to as a right-left direction. The direction in which boom 5 extends or the longitudinal direction of box-shaped structure body 19 (the direction perpendicular to the surface of the sheet of paper showing FIG. 3) is referred to as a front-rear direction. In the front-rear direction, the side on which boom 5 is coupled to revolving unit 3 corresponds to a rear direction while the side on which arm 6 is coupled to boom 5 corresponds to a front direction.

A boom cylinder attachment portion 17 is provided approximately in the center portion of each of left side plate 12 and right side plate 13 in the front-rear direction. The leading end of the boom cylinder for driving boom 5 is coupled to boom cylinder attachment portion 17. An arm cylinder attachment portion 18 is provided approximately in the center portion in the front-rear direction on the upper surface side of top plate 11. The base end of the arm cylinder for driving arm 6 is coupled to arm cylinder attachment portion 18.

Each of top plate 11, left side plate 12, right side plate 13, and bottom plate 14 may be formed of one plate material. Alternatively, a plurality of plate materials may be joined to one another by welding or the like to thereby form each of top plate 11, left side plate 12, right side plate 13, and bottom plate 14. A reinforcement member for enhancing the strength of boom 5 may be disposed in the internal space of box-shaped structure body 19.

FIG. 4 is an enlarged perspective view of a region IV in FIG. 2. As shown in FIG. 4, left side plate 12 is formed in a flat plate shape. Left side plate 12 has a surface 31 that forms the outer surface of box-shaped structure body 19 shown in FIG. 3, and a side surface 32 that faces boom foot bracket 15. Surface 31 is formed in a planar shape. Side surface 32 extends approximately orthogonal to surface 31.

Top plate 11 has a surface 21, a back surface 22 on the opposite side of surface 21, a side surface 23, and an end face 24. FIG. 5 is an enlarged perspective view showing a part of top plate 11. In the range of the partial view of top plate 11 shown in each of FIGS. 4 and 5, top plate 11 has a flat plate shape, and surface 21 and back surface 22 each have a planar shape. Surface 21 forms the outer surface of box-shaped structure body 19 shown in FIG. 3. Back surface 22 forms the inner surface of box-shaped structure body 19 shown in FIG. 3. Side surface 23 is continuous with surface 21 and back surface 22. Side surface 23 is approximately orthogonal to surface 21 and back surface 22.

End face 24 forms the rear end face of top plate 11. End face 24 is formed as a tapered surface inclined with respect to the thickness direction of top plate 11. The boundary portion between back surface 22 and end face 24 is located more rearward in the front-rear direction than the boundary portion between surface 21 and end face 24. End face 24 is inclined with a downward slope from surface 21 toward back surface 22. End face 24 is continuous with each of surface 21 and back surface 22.

Top plate 11 is provided with a cutout portion 28 obtained by cutting out a part of side surface 23. The length of top plate 11 in the right-left direction is reduced by cutout portion 28. Side surface 23 has cutout forming surfaces 25 and 26. Cutout forming surfaces 25 and 26 form the wall surface of cutout portion 28. Cutout forming surfaces 25 and 26 extend in the thickness direction of top plate 11.

Cutout forming surface 25 is formed in a planar shape extending in the front-rear direction. Cutout forming surface 26 is formed in a planar shape that is inclined with respect to the front-rear direction. Cutout forming surface 25 is continuous with end face 24. Cutout forming surface 25 is provided between end face 24 and cutout forming surface 26. Cutout forming surfaces 25 and 26 each are continuous with surface 21 and back surface 22. Cutout forming surfaces 25 and 26 each are approximately orthogonal to surface 21 and back surface 22.

FIG. 6 is a perspective view showing the configuration of boom foot bracket 15. Boom foot bracket 15 is a cast product formed by casting, for example, which is a metal cast product such as cast steel or weldable cast iron. Boom foot bracket 15 is integrally molded. As shown in FIG. 6, boom foot bracket 15 has a mount surface 59 on which top plate 11 is mounted.

As shown in FIGS. 4 and 6, boom foot bracket 15 has a rear wall portion 51. Rear wall portion 51 protrudes upward with respect to mount surface 59. Rear wall portion 51 extends in the right-left direction. Rear wall portion 51 has a bank shape. Rear wall portion 51 has a facing surface 52 that faces end face 24 of top plate 11. Facing surface 52 extends along end face 24 at a distance from end face 24. The distance between facing surface 52 and end face 24 increases gradually with increasing distance upward from mount surface 59.

Boom foot bracket 15 has an extending portion 54. Extending portion 54 protrudes upward with respect to mount surface 59. Extending portion 54 extends in the front-rear direction. Extending portion 54 extends in the longitudinal direction of box-shaped structure body 19 shown in FIG. 3. Extending portion 54 extends frontward from rear wall portion 51 to a leading end 55. Leading end 55 corresponds to a leading end portion of extending portion 54 in the longitudinal direction of box-shaped structure body 19. Extending portion 54 has a bank shape formed such that the protrusion height decreases toward leading end 55.

Extending portion 54 and side surface 23 of top plate 11 face each other at a distance from each other. Extending portion 54 faces a portion provided with cutout portion 28 in top plate 11. Extending portion 54 faces cutout forming surfaces 25 and 26 of top plate 11.

A recess portion 56 formed as a partial recess in boom foot bracket 15 is formed along extending portion 54. Recess portion 56 is recessed with respect to mount surface 59. In the state shown in FIG. 4 where top plate 11 is mounted on mount surface 59, recess portion 56 is formed between extending portion 54 and side surface 23 of top plate 11 that faces extending portion 54. Recess portion 56 is formed between extending portion 54 and cutout forming surfaces 25 and 26 of top plate 11.

A groove preparation surface 57 is formed to be continuous with recess portion 56. Groove preparation surface 57 is inclined with respect to mount surface 59. Groove preparation surface 57 is formed forward of recess portion 56. An edge portion 58 forms a boundary between groove preparation surface 57 and mount surface 59. Edge portion 58 extends in the front-rear direction.

Groove preparation surface 57 is formed at a portion that faces back surface 22 of top plate 11 in the state where top plate 11 is mounted on mount surface 59. Groove preparation surface 57 faces back surface 22 of top plate 11 and is formed in non-parallel with back surface 22. A groove is formed between groove preparation surface 57 and back surface 22. The groove width between groove preparation surface 57 and back surface 22 increases gradually with increasing distance from edge portion 58.

Due to formation of groove preparation surface 57, boom foot bracket 15 has a portion formed to be recessed with respect to mount surface 59. At the foremost portion of this recessed shape, a facing surface 60 that faces side surface 32 of left side plate 12 is formed. Facing surface 60 is formed in non-parallel with side surface 32 of left side plate 12. A groove is formed between facing surface 60 and side surface 32. The groove width between facing surface 60 and side surface 32 in the thickness direction of left side plate 12 increases gradually toward surface 31 of left side plate 12.

FIG. 7 is a plan view of region IV in FIG. 2. FIG. 7 shows a diagram of top plate 11 and boom foot bracket 15 as seen from the direction perpendicular to surface 21 of top plate 11. The up-down direction in FIG. 7 corresponds to the above-described right-left direction while the right-left direction in FIG. 7 corresponds to the above-described front-rear direction.

As shown in FIG. 7, extending portion 54 has a facing surface 61 that faces side surface 23 of top plate 11, more specifically, that faces cutout forming surfaces 25 and 26. Facing surface 61 extends along side surface 23 of top plate 11 at a distance from top plate 11. Cutout portion 28 of top plate 11 is formed in the longitudinal direction of box-shaped structure body 19 so as to extend from end face 24 of top plate 11 beyond leading end 55 of extending portion 54. The length of cutout portion 28 formed in top plate 11 is greater in the front-rear direction than the length of extending portion 54. Leading end 55 of extending portion 54 faces cutout forming surface 26.

Cutout forming surface 25 defining a part of the boundary of cutout portion 28 and edge portion 58 are continuous with each other when seen from the direction perpendicular to surface 21 of top plate 11. Cutout forming surface 25 and edge portion 58 are flush with each other as seen in the thickness direction of top plate 11. Cutout forming surface 25 and edge portion 58 extend along a straight line in the front-rear direction in a top view shown in FIG. 7.

Left side plate 12 has surface 31 shown in FIG. 4 and a back surface 33 on the opposite side of surface 31. When seen from the direction perpendicular to surface 21 of top plate 11, edge portion 58 and back surface 33 of left side plate 12 may be arranged in parallel with each other. In the right-left direction, edge portion 58 may be provided between surface 31 and back surface 33 of left side plate 12.

FIG. 8 is a side view of region IV in FIG. 2. FIG. 8 shows a diagram of top plate 11 and boom foot bracket 15 as seen in the direction indicated by an arrow VIII in FIG. 7. In addition, FIG. 7 shows a diagram of top plate 11 and boom foot bracket 15 as seen in the direction indicated by an arrow VII in FIG. 8. The up-down direction in FIG. 8 corresponds to the above-described up-down direction while the right-left direction in FIG. 8 corresponds to the above-described front-rear direction.

In a side view shown in FIG. 8, extending portion 54 of boom foot bracket 15 covers a part of side surface 23 of top plate 11, more specifically, a part of each of cutout forming surfaces 25 and 26. Cutout portion 28 is formed in a portion of side surface 23 of top plate 11 that faces extending portion 54. When top plate 11 and boom foot bracket 15 are seen in the right-left direction, extending portion 54 partially overlaps with cutout forming surfaces 25 and 26. When seen in the direction perpendicular to surface 31 of left side plate 12, or seen in the thickness direction of left side plate 12, a part of extending portion 54 overlaps with a part of side surface 23 of top plate 11. Extending portion 54 has a portion that faces side surface 23 of top plate 11.

FIG. 9 is a perspective view showing the state where top plate 11 and boom foot bracket 15 are welded to each other. FIG. 10 is a perspective view showing the state where top plate 11 and boom foot bracket 15 are welded to each other, as seen at a different angle.

The first groove is formed between facing surface 52 of boom foot bracket 15 and end face 24 of top plate 11. The second groove is formed between facing surface 61 of extending portion 54 in boom foot bracket 15 and side surface 23 of top plate 11, more specifically, cutout forming surfaces 25 and 26. The third groove is formed between groove preparation surface 57 of boom foot bracket 15 and back surface 22 of top plate 11.

The first groove, the second groove and the third groove form a weld portion between top plate 11 and boom foot bracket 15. End face 24 of top plate 11 forms the first groove. Recess portion 56 is formed in the bottom surface of the second groove. Edge portion 58 of groove preparation surface 57 forms a bottom portion of the third groove. FIGS. 9 and 10 each show a weld bead 101 formed by welding top plate 11 and boom foot bracket 15 along the first groove, the second groove and the third groove.

The first groove is continuous with the second groove. The second groove is continuous with the third groove. Top plate 11 and boom foot bracket 15 can be welded in a series of the first groove, the second groove and the third groove in this order. The first groove is welded in the state where the opening of the first groove is directed upward. When welding reaches the terminal end of the first groove, top plate 11 and boom foot bracket 15 are integrally rotated in the direction indicated by an arrow shown in FIG. 10. Then, the opening of the second groove is directed upward, in which state the second groove is welded. When welding reaches the terminal end of the second groove, top plate 11 and boom foot bracket 15 are further rotated in the direction indicated by the arrow shown in FIG. 10. Then, the opening of the third groove is directed upward, in which state the third groove is welded. In this way, the first, second and third grooves are sequentially welded, so that top plate 11 and boom foot bracket 15 are joined to each other.

By attaching top plate 11 and boom foot bracket 15 to a positioner of a welding robot, top plate 11 and boom foot bracket 15 can be automatically integrally rotated. When the first groove is welded, top plate 11 is disposed so as to extend approximately in the horizontal direction. When the second groove is welded, top plate 11 is disposed so as to be inclined with respect to the horizontal direction and the vertical direction. When the third groove is welded, top plate 11 is disposed approximately in the vertical direction.

The fourth groove is formed between side surface 32 of left side plate 12 and facing surface 60 of boom foot bracket 15. The fifth weld portion that is welded by fillet welding is formed between back surface 22 of top plate 11 and surface 31 of left side plate 12. Weld bead 111 shown in FIG. 3 represents a weld bead obtained by welding back surface 22 of top plate 11 and surface 31 of left side plate 12 by fillet welding.

When welding reaches the terminal end of the third groove, then, the fourth groove or the fifth weld portion is welded. The first, second and third grooves are welded repeatedly several times in order to sufficiently ensure the throat depth. In a series of welding operations, until welding of the fourth groove is completed, welding of the third groove may be followed by welding of the fourth groove. Then, welding of the third groove may be followed by welding of the fifth weld portion. In this way, welding of the first to third grooves is followed by continuous welding of the fourth groove or the fifth weld portion, with the result that boom foot bracket 15 and left side plate 12 are joined to each other while top plate 11 and left side plate 12 are joined to each other.

The characteristic configurations of the present embodiment will be set forth below though a part of the configurations may be repeatedly described. Boom 5 in the present embodiment corresponds to boom 5 used in hydraulic excavator 100 shown in FIG. 1 and includes top plate 11, left side plate 12, right side plate 13, and bottom plate 14, as shown in FIGS. 2 and 3. Left side plate 12 is joined to top plate 11. Right side plate 13 is joined to the top plate and faces left side plate 12 at a distance from left side plate 12. Bottom plate 14 is joined to left side plate 12 and right side plate 13, and faces top plate 11 at a distance from top plate 11. Top plate 11, left side plate 12, right side plate 13, and bottom plate 14 are joined to one another to form box-shaped structure body 19 shown in FIG. 3. Top plate 11, left side plate 12, right side plate 13, and bottom plate 14 in the embodiment correspond to the first plate material, the second plate material, the third plate material, and the fourth plate material, respectively.

Boom 5 further includes boom foot bracket 15, as shown in FIG. 2. Boom foot bracket 15 is joined to each of top plate 11, left side plate 12, right side plate 13, and bottom plate 14 at the end of box-shaped structure body 19 shown in FIG. 3 in its longitudinal direction. As shown in FIGS. 4 and 6 to 8, boom foot bracket 15 has extending portion 54. Extending portion 54 extends in the longitudinal direction of box-shaped structure body 19. Extending portion 54 has a portion that faces side surface 23 of top plate 11, as shown in FIGS. 4, 7 and 8. Boom foot bracket 15 in the embodiment corresponds to the first attachment member.

When the first groove formed of end face 24 of top plate 11 and facing surface 52 of boom foot bracket 15 is welded, molten metal is dammed up due to existence of extending portion 54. Since extending portion 54 is provided and extending portion 54 functions as a dam to prevent an overflow of molten metal during the welding operation, a sufficient throat depth can be ensured when the first groove is welded. Thereby, the number of steps required for the welding operation of the first groove can be reduced while the welding quality for the first groove can be improved.

The second groove is formed of side surface 23 of top plate 11 and facing surface 61 of extending portion 54. The first groove and the second groove are formed to communicate with each other. Thereby, welding can be smoothly shifted from the first groove to the second groove. Since the first groove and the second groove can be continuously welded, the number of steps required for the welding operation can be reduced. The first groove and the second groove can be continuously welded using a welding robot, thereby allowing stabilized welding, so that the welding quality can be improved.

Also as shown in FIGS. 4, 5, 7, and 8, cutout portion 28 is formed in the portion of top plate 11 that faces extending portion 54. The second groove is formed of: cutout forming surfaces 25 and 26 in side surface 23 of top plate 11, which form cutout portion 28; and facing surface 60 of extending portion 54. The third groove is formed of back surface 22 of top plate 11 and groove preparation surface 57 of boom foot bracket 15. By forming cutout portion 28 in top plate 11, the second groove and the third groove can be formed to communicate with each other, so that welding can be smoothly shifted from the second groove to the third groove. Since the second groove and the third groove can be continuously welded, the number of steps required for the welding operation can be reduced. The second groove and the third groove can be continuously welded using a welding robot, which allows stabilized welding, so that the welding quality can be improved.

Also as shown in FIGS. 4 and 8, top plate 11 has surface 21 and back surface 22 on the opposite side of surface 21. Surface 21 forms the outer surface of box-shaped structure body 19 shown in FIG. 3. Surface 21 in the embodiment corresponds to the first surface while back surface 22 corresponds to the first back surface. As shown in FIGS. 6 to 8, groove preparation surface 57 is formed in a portion of boom foot bracket 15 that faces back surface 22 of top plate 11. Together with back surface 22, groove preparation surface 57 forms the third groove. Edge portion 58 of groove preparation surface 57 forms the bottom portion of the third groove. As shown in FIG. 7, cutout forming surface 25 and edge portion 58 are continuous with each other, as seen from the direction perpendicular to surface 21 of top plate 11.

Cutout forming surface 25 and edge portion 58 are provided flush with each other, so that smooth shifting of welding from the second groove to the third groove can be further more facilitated. Since the second groove and the third groove can be continuously welded with more reliability, the number of steps required for the welding operation can be reduced while the welding quality can be improved.

Also as shown in FIGS. 7 and 8, cutout portion 28 is formed to extend from end face 24 of top plate 11 beyond leading end 55 of extending portion 54. By defining the range in which cutout portion 28 is formed in this way, it becomes possible to avoid interference of extending portion 54 with the nozzle at the end of a welding machine when welding is shifted from the second groove to the third groove. Accordingly, smooth shifting of welding from the second groove to the third groove can be further more facilitated.

Also as shown in FIGS. 4 and 6, recess portion 56 formed as a partial recess in the surface of boom foot bracket 15 is provided between extending portion 54 and side surface 23 of top plate 11 that faces extending portion 54. When the first groove, the second groove and the third groove are continuously welded, top plate 11 and boom foot bracket 15 need to be rotated during welding. By providing recess portion 56, molten metal can be accumulated in recess portion 56 during rotation, so that it becomes possible to implement the configuration in which molten metal is further less likely to overflow during the welding operation. By filling up recess portion 56 by welding, flat weld bead 101 can be obtained while the throat depth required for the second groove can be ensured.

Also as shown in FIGS. 4, 6 and 8, extending portion 54 has a bank shape formed such that the protrusion height decreases toward leading end 55. By defining the shape of extending portion 54 in this way, it becomes possible to avoid interference of extending portion 54 with the nozzle at the end of a welding machine when welding is shifted from the second groove to the third groove. Accordingly, smooth shifting of welding from the second groove to the third groove can be further more facilitated.

In boom 5 in the present embodiment having the configuration as described above, the weld line can be formed to extend continuously from the first groove to the third groove, so that continuous welding can be performed using a welding robot. Accordingly, the number of steps required for the welding operation can be reduced while the welding quality can be improved. The corner portion of boom 5 at which a stress concentration is more likely to occur is automatically continuously welded, to thereby improve the welding quality, so that the strength of boom 5 can be enhanced.

Preferably, boom foot bracket 15 is a cast product. Complicatedly-shaped boom foot bracket 15 including extending portion 54, recess portion 56, groove preparation surface 57 and the like is integrally molded by casting using an appropriate metal mold prepared in advance, so that this boom foot bracket 15 can readily be molded. Thus, the number of steps required for molding boom foot bracket 15 can be reduced while variations in shape of the molded product can be reduced.

In the above-described embodiment, welding between top plate 11 and boom foot bracket 15 in boom 5 of work implement 4 has been described. The present invention can be applicable also to the case where arm 6 of work implement 4 is molded by welding. Work implement 4 of hydraulic excavator 100 that is an object of the present invention refers to boom 5 and arm 6.

FIG. 11 is a side view showing the schematic configuration of arm 6 shown in FIG. 1. As shown in FIG. 11, arm 6 has a top plate 71, a bottom plate 74, an arm cylinder attachment bracket 75, and an arm top bracket 76. Arm cylinder attachment bracket 75 is joined at one end of arm 6 in its longitudinal direction to top plate 71 and bottom plate 74. Arm top bracket 76 is joined at the other end of arm 6 in its longitudinal direction to top plate 71 and bottom plate 74. Arm cylinder attachment bracket 75 forms the rear end portion of arm 6 while arm top bracket 76 forms the front end portion of arm 6. Arm top bracket 76 is a cast product molded by casting.

A boom connection hole 77 is formed at the position in the vicinity of arm cylinder attachment bracket 75 in the longitudinal direction of arm 6. Arm attachment bracket 16 shown in FIG. 3 is coupled to boom connection hole 77.

The same configurations as those of boom foot bracket 15 and top plate 11 described above are applied to the welding portion between arm top bracket 76 and top plate 71, so that the number of steps required for the welding operation can be reduced while the welding quality can be improved.

It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the meaning and scope equivalent to the terms of the claims.

REFERENCE SIGNS LIST

4 work implement, 5 boom, 6 arm, 11 top plate, 12 left side plate, 13 right side plate, 14 bottom plate, 15 boom foot bracket, 19 box-shaped structure body, 21, 31 surface, 22, 33 back surface, 23, 32 side surface, 24 end face, 25, 26 cutout forming surface, 28 cutout portion, 51 rear wall portion, 52, 60, 61 facing surface, 54 extending portion, 55 leading end, 56 recess portion, 57 groove preparation surface, 58 edge portion, 59 mount surface, 76 arm top bracket, 100 hydraulic excavator, 101, 111, 112, 113, 114 weld bead. 

1. A work implement of a hydraulic excavator, the work implement comprising: a first plate material; a second plate material joined to the first plate material; a third plate material joined to the first plate material and facing the second plate material at a distance from the second plate material; and a fourth plate material joined to the second plate material and the third plate material and facing the first plate material at a distance from the first plate material, the first plate material, the second plate material, the third plate material, and the fourth plate material being joined to one another to form a box-shaped structure body, the work implement further comprising a first attachment member joined to each of the first plate material, the second plate material, the third plate material, and the fourth plate material at an end of the box-shaped structure body in a longitudinal direction of the box-shaped structure body, the first attachment member including an extending portion that extends in the longitudinal direction of the box-shaped structure body, the extending portion including a portion that faces a side surface of the first plate material.
 2. The work implement of a hydraulic excavator according to claim 1, wherein a cutout portion is provided in a portion of the first plate material that faces the extending portion.
 3. The work implement of a hydraulic excavator according to claim 2, wherein the first plate material includes a first surface that forms an outer surface of the box-shaped structure body, and a first back surface on an opposite side of the first surface, a portion of the first attachment member that faces the first back surface is provided with a groove preparation surface that forms a groove together with the first back surface, and a portion of the side surface that includes the cutout portion in the first plate material and a bottom portion of the groove are continuous with each other when seen from a direction perpendicular to the first surface.
 4. The work implement of a hydraulic excavator according to claim 2, wherein the cutout portion is formed in the longitudinal direction of the box-shaped structure body so as to extend from an end of the first plate material beyond a leading end of the extending portion in the longitudinal direction.
 5. The work implement of a hydraulic excavator according to claim 1, wherein the extending portion has a bank shape formed such that a protrusion height decreases toward a leading end of the extending portion in the longitudinal direction.
 6. The work implement of a hydraulic excavator according to claim 1, wherein the first attachment member is a cast product.
 7. A method of manufacturing a work implement of a hydraulic excavator, the work implement including: a first plate material; a second plate material joined to the first plate material; a third plate material joined to the first plate material and facing the second plate material at a distance from the second plate material; and a fourth plate material joined to the second plate material and the third plate material and facing the first plate material at a distance from the first plate material, the first plate material, the second plate material, the third plate material, and the fourth plate material being joined to one another to form a box-shaped structure body, the work implement further including a first attachment member joined to each of the first plate material, the second plate material, the third plate material, and the fourth plate material at an end of the box-shaped structure body in a longitudinal direction of the box-shaped structure body, the first attachment member including an extending portion that extends in the longitudinal direction of the box-shaped structure body, the extending portion including a portion that faces a side surface of the first plate material, the method comprising: forming a recess portion as a partial recess in a surface of the first attachment member, the recess portion being located between the extending portion and the side surface of the first plate material that faces the extending portion; and filling up the recess portion by welding. 